The primary goal of this research is the reduction in the number of cancer- free patients required to undergo open (surgical) biopsy because of equivocal mammographic findings. A second goal is the reduction of local recurrence in patients with breast cancer who are receiving breast- conserving treatment. These goals will be achieved with the use of a low-cost noninvasive device to differentiate, with high confidence levels, between malignant tumors and benign tissues in the breast. The device will aid in treatment planning and in surgical resection by defining tumor margins. The proposed phase I study addresses the design of the device. Plans for later phases of the study include prototype fabrication, clinical trials and commercial production of the device. In the long-term, the research will reduce the morbidity and health care costs associated with unnecessary biopsies and locally recurrent breast cancer.